An Evaluation of the Proposed Spratly Islands Impact Structure
In November 3, 2013, on the “Cosmic Tusk,” Hermann G W Burchard proposed that the region underlying the Spratly Islands is the center of a multi-ring circular to oval impact structure,
informally called “Crater Burchard,” that has a diameter of about 275 km (175 miles). Given that crater are not normally named after people, but after geographic locations, this proposed
impact structure will be referred to as the “Spratly Islands Impact Structure” for purposes of discussion after the Spratly Islands in the South China Sea. The center of this proposed
275 km (175 miles) in diameter impact structure is an atoll called Union Reefs, or Union Bank at Latitude 9.788666° and Longitude 114.351768°. Burchard speculates that the Union Reefs atoll might lie on top of the top of the central uplift of
such an impact crater. he further speculates that this proposed crater might be the long searched for Australasian tektite impact crater Burchard (2013). The existence of this impact structure
is based entirely upon hypothetical circular features found by the visual examination of bathymetry as portrayed by Google Earth.
The Spratly Islands is part of a larger area called the "Dangerous Ground." The Dangerous Ground is a part of southeast South China Sea that is characterized numerous low islands, reefs,
submerged banks, shoals, and atolls that often rise abruptly from the depths of the South China Sea. Because this area is poorly and inconsistently charted, it was, and in part still is, a dangerous
place for navigation. Tropical depression, typhoons, unpredictable squalls, modern day pirates, and armed naval vessels involved in various international jurisdictional disputes are additional hazards
found within this region (Anonymous 2011).
Burchard (2013) is right about there being significant information (“news”) about the geology of the Spratly Islands and adjacent Dangerous Ground having been collected because of the oil and
gas potential of the area. Contrary to what he assumed, specifics about the geology of region were quite easy to locate and were collected in only a few hours of effort. In addition to geological
research associated with oil and gas studies, detailed geological data for this part of the South China Sea was gathered during Ocean Drilling Program (ODP) Leg 184 (Shipboard Scientific
Party 2000a). Thus, the published data available for the Spratly Islands and adjacent Dangerous Ground includes seismic lines that cut across the proposed impact structure and an ODP drillhole,
ODP Site 1143 of Leg 184, that lies just within the alleged rim of the proposed Spratly Islands Impact Structure. The drillhole at ODP Site 1143 was continuously cored to from the sea floor
at a depth of 2772 m below sea level to a depth of 512.4 m (1,680 feet) below the sea bottom (Shipboard Scientific Party, 2000b).
Because of their potential oil and gas potential and the multiple and contentious international claims and jurisdictional disputes concerning the Spratly Islands and adjacent Dangerous Ground
region, they have been the subject of intensive and repetitive geological studies from a wide variety of governmental and nongovernmental agencies and private corporations of various
nationalities. Although much of the data, including seismic lines and drillhole data, remain proprietary, scientifically significant and revealing data, including regional multi-channel seismic
data, and their interpretations, have been published in sufficient number to provide a clear picture of their geology as discussed in Blanche and Blanche (1997), Hutchison (2004, 2010),
Hutchison and Vijayan (2010), Hinz and Schlueter (1985), Metcalfe (2010), Wei-Weil and Jia-Biao (2011), Zhen etal (2011) and various other publications.
The above research found that at the surface the Spratly Islands consist of reefs, banks, and shoals that are composed of biogenic carbonate that have accumulated on the higher crests of major sea-floor seafloor ridges. These ridges consist of a series of uplifted fault-blocks, called horsts, which are part of a series of parallel and en echelon, half-grabens and rotated
fault-blocks. The axes of the ridge crests (horsts) and their associated grabens form well-defined linear trends that lie parallel to magnetic anomalies of the contiguous oceanic crust of the adjacent South China Sea. These fault-blocks consist of Triassic, Jurassic, and Cretaceous strata that include calcalkalic extrusive rocks, intermediate to acid intrusive rocks, sandstones, siltstones, dark-green claystones, and metamorphic rocks that include biotite-muscovite-feldspar-quartz migmatites or
gamet-micaschists (Blanche and Blanche 1997, Hutchison 2004, 2010, Hutchison and Vijayan 2010, Hinz and Schlueter 1985, Wei-Weil and Jia-Biao 2011).
These horsts and grabens are the result of two distinct periods of tectonic stretching of continental crust along underlying deeply-rooted detachment faults. The early period of tectonism
occurred during the Late Cretaceous and Early Oligocene and resulted in the formation of horsts, half-grabens, and rotated fault-blocks. This tectonism was associated with the rifting and stretching of continental crust that corresponded with the initial sea-floor spreading within the South China Sea. Further stretching and block faulting of continental crust occurred within the Spratly Islands and adjacent Dangerous Ground area during the Late Oligocene-Early Miocene and eventually halted
afterwards. After tectonic activity had ceased, the crest of the horsts that lay in shallow water were colonized and biogenic carbonates accumulated on them to form reefs, shoals and
cays known as the Spratly Islands (Wei-Weil and Jia-Biao 2011, Zhen et al. 2011)
The history of faulting and related tectonism within the Spratly Islands and adjacent Dangerous Ground region can be confidently reconstructed on the basis of regional unconformities that can be
clearly seen and identified in regional and local seismic sections. Because they have been dated using biostratigraphy in drillholes that intersect them, they form timelines that can be traced using
seismic across the entire Dangerous Ground region, including the Spratly Islands. The most important of these unconformities is known as either the “Mid-Miocene,” "Breakup," or “T60"
unconformity (Hutchison 2004, Hutchison and Vijayan 2010, Wei-Wei and Jia-Biao 2011, Zhen et al. 2011). This unconformity is an angular unconformity that separates syn-rift strata, which
accumulated during the faulting that formed these regional half-grabens and rotated blocks, from post-rift strata, which accumulated after the regional tectonism had ceased during the Early Miocene. The T60 unconformity clearly demonstrates that faulting within Spratly Islands and Dangerous Ground had ended by Early Miocene (Hutchison and Vijayan 2010, Wei-Wei
and Jia-Biao 2011, Zhen et al. 2011). Thus, there is complete absence of either any significant faulting or any other tectonism that can be associated with a 0.78 Ma extraterrestrial impact. The
relatively undisturbed and intact nature of post- Early Miocene sediments within the Spratly Islands and Dangerous Ground region completely refutes any hypothesis about they being the site of a
relatively large 0.78 Ma extraterrestrial impact being associated with the Spratly Islands and Dangerous Ground region.
Equally revealing are the cores recovered from drilling at ODP Site 1143. The examination of these cores by Shipboard Scientific Party (2000b) found only one recognizable lithologic unit, which
is subdivided into two subunits, Subunits, IA and IB, within the 512 m-long (1,780 foot-long) core. The upper 160 m (525 feet) of the sedimentary sequence, Subunit 1A, consists of typically massive, olive-gray, light grayish green, hemipelagic, calcareous clay with abundant nannofossils and foraminifera. Distinct green clay layers are present. Foraminifer ooze turbidites were also occur
within this subunit. The turbidites are normally graded. They often exhibit a scoured basal contact. The part of the sedimentary sequence that is below 160 m (525 feet), Subunit 1B, consists
of are clayey nannofossil mixed sediment, nannofossil clay, and nannofossil ooze with clay. This subunit has a higher carbonate content; more turbidites; and fewer green clay layers then
Subunit 1A. In addition, it contains infrequent dark gray volcanic ash layers and volcanic breccias. Subunit 1B also exhibits trace fossils, such as Zoophycos and Chondrites, and sedimentary
structures associated with slumps and turbidites (Shipboard Scientific Party 2000b).
These sediments can be readily dated from the abundant microfossils, including nannofossils and foraminifera. These fossils demonstrate that the Pleistocene/ Pliocene boundary is
located between 93.5 and 94.3 m (307 and 309 feet) below the sea bottom and the Pliocene/Miocene boundary is located between 213.0 and 200.6 m (699 and 658 feet) below the sea bottom. In addition, a clear paleomagentic declination change of nearly 180° at 43.2 m (142 feet) below sea bottom and in the middle of Core 184-1143C-5H was interpreted to represent the Brunhes/Matuyama reversal at about 0.78 Ma. The sedimentary sequence cored at ODP Site 1143 clearly shows that hemipelagic
sedimentation of fine-grained terrigenous material and calcareous nannofossils occurred essentially uninterrupted from the late Miocene to present at this site (Shipboard Scientific Party
2000b).
Being located just within the rim of the proposed Spratly Islands Impact Structure, this core, as does published seismic sections, demonstrates the lack of any significant Pleistocene-age
extraterrestrial impact structure being associated with the Spratly Islands. The ODP Site1143 cores, seismic data, and other published research effectively refute the existence of the
proposed Spratly Islands Impact Structure and relegates it to a long of imaginary extraterrestrial impact structures that have been proposed solely on the basis of remote sensing data. It
shows how dubious a methodology using Google Earth alone to identify extraterrestrial impact craters.
Note: For other examples of the dubious use of Google Earth to identify extraterrestrial impact structures, go read
1. The Manuel Benavides Craterwrong and Cratermania
http://www.mail-archive.com/meteorite-list@meteoritecentral.com/msg92117.html
2. Preliminary Evaluation of a Proposed “Younger Dryas
Impact” Crater
https://www.mail-archive.com/meteorite-list@meteoritecentral.com/msg102013.html
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Yours,
Paul H.
